Up to ordinary heights, the change in the distance of a projectile from the centre of the earth is negligible small, as compared to the radius of the earth, Due to which the projectile moves under a uniform gravitational force and its path is parabolic.
But if projectile is going to a very great height, the gravitational force decreases, which is inversely proportional to the square of the distance of the projectile from the centre of the earth. Under such a variable force, the path of projectile is elliptical.